.\"	$OpenBSD: RSA_set_method.3,v 1.4 2016/12/02 19:28:41 jmc Exp $
.\"	OpenSSL 99d63d46 Oct 26 13:56:48 2016 -0400
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.Dd $Mdocdate: December 2 2016 $
.Dt RSA_SET_METHOD 3
.Os
.Sh NAME
.Nm RSA_set_default_method ,
.Nm RSA_get_default_method ,
.Nm RSA_set_method ,
.Nm RSA_get_method ,
.Nm RSA_PKCS1_SSLeay ,
.Nm RSA_null_method ,
.Nm RSA_flags ,
.Nm RSA_new_method ,
.Nm RSA_get_default_openssl_method ,
.Nm RSA_set_default_openssl_method
.Nd select RSA method
.Sh SYNOPSIS
.In openssl/rsa.h
.Ft void
.Fo RSA_set_default_method
.Fa "const RSA_METHOD *meth"
.Fc
.Ft RSA_METHOD *
.Fn RSA_get_default_method void
.Ft int
.Fo RSA_set_method
.Fa "RSA *rsa"
.Fa "const RSA_METHOD *meth"
.Fc
.Ft RSA_METHOD *
.Fo RSA_get_method
.Fa "const RSA *rsa"
.Fc
.Ft RSA_METHOD *
.Fn RSA_PKCS1_SSLeay void
.Ft RSA_METHOD *
.Fn RSA_null_method void
.Ft int
.Fo RSA_flags
.Fa "const RSA *rsa"
.Fc
.Ft RSA *
.Fo RSA_new_method
.Fa "RSA_METHOD *meth"
.Fc
.Sh DESCRIPTION
An
.Vt RSA_METHOD
specifies the functions that OpenSSL uses for RSA operations.
By modifying the method, alternative implementations such as hardware
accelerators may be used.
See the
.Sx CAVEATS
section for how these RSA API functions are affected by the use of
.Xr engine 3
API calls.
.Pp
Initially, the default
.Vt RSA_METHOD
is the OpenSSL internal implementation, as returned by
.Fn RSA_PKCS1_SSLeay .
.Pp
.Fn RSA_set_default_method
makes
.Fa meth
the default method for all
.Vt RSA
structures created later.
.Sy NB :
This is true only whilst no
.Vt ENGINE
has been set as a default for RSA, so this function is no longer
recommended.
.Pp
.Fn RSA_get_default_method
returns a pointer to the current default
.Vt RSA_METHOD .
However, the meaningfulness of this result is dependent on whether
the
.Xr engine 3
API is being used, so this function is no longer recommended.
.Pp
.Fn RSA_set_method
selects
.Fa meth
to perform all operations using the key
.Fa rsa .
This will replace the
.Vt RSA_METHOD
used by the RSA key, and if the previous method was supplied by an
.Vt ENGINE ,
the handle to that
.Vt ENGINE
will be released during the change.
It is possible to have RSA keys that only work with certain
.Vt RSA_METHOD
implementations (e.g. from an
.Vt ENGINE
module that supports embedded hardware-protected keys),
and in such cases attempting to change the
.Vt RSA_METHOD
for the key can have unexpected results.
.Pp
.Fn RSA_get_method
returns a pointer to the
.Vt RSA_METHOD
being used by
.Fa rsa .
This method may or may not be supplied by an
.Vt ENGINE
implementation but if it is, the return value can only be guaranteed
to be valid as long as the RSA key itself is valid and does not
have its implementation changed by
.Fn RSA_set_method .
.Pp
.Fn RSA_flags
returns the flags that are set for the current
.Vt RSA_METHOD
of
.Fa rsa .
See the
.Sx BUGS
section.
.Pp
.Fn RSA_new_method
allocates and initializes an
.Vt RSA
structure so that
.Fa meth
will be used for the RSA operations.
If
.Sy engine
is NULL, the default ENGINE for RSA operations is used and, if no
default ENGINE is set, the RSA_METHOD controlled by
.Fn RSA_set_default_method
is used.
.Pp
.Fn RSA_flags
returns the
.Sy flags
that are set for
.Fa rsa Ns 's
current method.
.Pp
.Fn RSA_new_method
allocates and initializes an
.Vt RSA
structure so that
.Fa meth
will be used for the RSA operations.
If
.Fa meth
is
.Dv NULL ,
the default method is used.
.Sh THE RSA_METHOD STRUCTURE
.Bd -literal
typedef struct rsa_meth_st
{
     /* name of the implementation */
	const char *name;

     /* encrypt */
	int (*rsa_pub_enc)(int flen, unsigned char *from,
          unsigned char *to, RSA *rsa, int padding);

     /* verify arbitrary data */
	int (*rsa_pub_dec)(int flen, unsigned char *from,
          unsigned char *to, RSA *rsa, int padding);

     /* sign arbitrary data */
	int (*rsa_priv_enc)(int flen, unsigned char *from,
          unsigned char *to, RSA *rsa, int padding);

     /* decrypt */
	int (*rsa_priv_dec)(int flen, unsigned char *from,
          unsigned char *to, RSA *rsa, int padding);

     /* compute r0 = r0 ^ I mod rsa->n (May be NULL for some
                                        implementations) */
	int (*rsa_mod_exp)(BIGNUM *r0, BIGNUM *I, RSA *rsa);

     /* compute r = a ^ p mod m (May be NULL for some implementations) */
	int (*bn_mod_exp)(BIGNUM *r, BIGNUM *a, const BIGNUM *p,
          const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *m_ctx);

     /* called at RSA_new */
	int (*init)(RSA *rsa);

     /* called at RSA_free */
	int (*finish)(RSA *rsa);

     /* RSA_FLAG_EXT_PKEY        - rsa_mod_exp is called for private key
      *                            operations, even if p,q,dmp1,dmq1,iqmp
      *                            are NULL
      * RSA_FLAG_SIGN_VER        - enable rsa_sign and rsa_verify
      * RSA_METHOD_FLAG_NO_CHECK - don't check pub/private match
      */
	int flags;

	char *app_data; /* ?? */

     /* sign. For backward compatibility, this is used only
      * if (flags & RSA_FLAG_SIGN_VER)
      */
	int (*rsa_sign)(int type, unsigned char *m, unsigned int m_len,
           unsigned char *sigret, unsigned int *siglen, RSA *rsa);

     /* verify. For backward compatibility, this is used only
      * if (flags & RSA_FLAG_SIGN_VER)
      */
	int (*rsa_verify)(int type, unsigned char *m, unsigned int m_len,
           unsigned char *sigbuf, unsigned int siglen, RSA *rsa);

} RSA_METHOD;
.Ed
.Sh RETURN VALUES
.Fn RSA_PKCS1_SSLeay ,
.Fn RSA_null_method ,
.Fn RSA_get_default_method
and
.Fn RSA_get_method
return pointers to the respective
.Vt RSA_METHOD .
.Pp
.Fn RSA_set_method
returns a pointer to the old
.Vt RSA_METHOD
implementation that was replaced.
However, this return value should probably be ignored because if it was
supplied by an
.Vt ENGINE ,
the pointer could be invalidated at any time if the
.Vt ENGINE
is unloaded.
In fact, it could be unloaded as a result of the
.Fn RSA_set_method
function releasing its handle to the
.Vt ENGINE .
For this reason, the return type may be replaced with a
.Vt void
declaration in a future release.
.Pp
.Fn RSA_new_method
returns
.Dv NULL
and sets an error code that can be obtained by
.Xr ERR_get_error 3
if the allocation fails.
Otherwise it returns a pointer to the newly allocated structure.
.Sh SEE ALSO
.Xr RSA_new 3
.Sh HISTORY
.Fn RSA_new_method
and
.Fn RSA_set_default_method
appeared in SSLeay 0.8.
.Fn RSA_get_default_method ,
.Fn RSA_set_method ,
and
.Fn RSA_get_method
as well as the
.Fa rsa_sign
and
.Fa rsa_verify
components of
.Vt RSA_METHOD
were added in OpenSSL 0.9.4.
.Pp
.Fn RSA_set_default_openssl_method
and
.Fn RSA_get_default_openssl_method
replaced
.Fn RSA_set_default_method
and
.Fn RSA_get_default_method
respectively, and
.Fn RSA_set_method
and
.Fn RSA_new_method
were altered to use
.Vt ENGINE Ns s
rather than
.Vt RSA_METHOD Ns s
during development of the
.Xr engine 3
version of OpenSSL 0.9.6.
For 0.9.7, the handling of defaults in the
.Xr engine 3
API was restructured so that this change was reversed, and behaviour
of the other functions resembled more closely the previous behaviour.
The behaviour of defaults in the
.Xr engine 3
API now transparently overrides the behaviour of defaults in the
RSA API without requiring changing these function prototypes.
.Sh CAVEATS
As of version 0.9.7,
.Vt RSA_METHOD
implementations are grouped together with other algorithmic APIs (e.g.\&
.Vt DSA_METHOD
or
.Vt EVP_CIPHER )
into
.Vt ENGINE
modules.
If a default
.Vt ENGINE
is specified for RSA functionality using an
.Xr engine 3
API function, that will override any RSA defaults set using the RSA
API, i.e.\&
.Fn RSA_set_default_method .
For this reason, the
.Xr engine 3
API is the recommended way to control default implementations for
use in RSA and other cryptographic algorithms.
.Sh BUGS
The behaviour of
.Fn RSA_flags
is a misfeature that is left as-is for now to avoid creating
compatibility problems.
RSA functionality, such as the encryption functions, are controlled by
the
.Fa flags
value in the
.Vt RSA
key itself, not by the
.Fa flags
value in the
.Vt RSA_METHOD
attached to the RSA key (which is what this function returns).
If the flags element of an
.Vt RSA
key is changed, the changes will be honoured by RSA functionality
but will not be reflected in the return value of the
.Fn RSA_flags
function - in effect
.Fn RSA_flags
behaves more like a RSA_default_flags() function, which does not
currently exist.
